Update receiveSize for resumed DCC receives

This makes it send the right ACK packets, which fixes resumes not finishing at all
Fixes issue 3726

Change-Id: Icc734b58080413c4e8afbc1ba7f251b585acfd3d
Reviewed-on: http://gerrit.dmdirc.com/841
Automatic-Compile: Chris Smith <chris@dmdirc.com>
Reviewed-by: Chris Smith <chris@dmdirc.com>
Automatic-Compile: DMDirc Local Commits <dmdirc@googlemail.com>

src/com/dmdirc/addons/dcc/DCCTransfer.java

@@ -298,14 +298,16 @@ public class DCCTransfer extends DCC {
      */
     public int setFileStart(final int startpos) {
         this.startpos = startpos;
+        this.readSize = startpos;
+
         if (transferType == TransferType.SEND && fileIn != null) {
             try {
                 this.startpos = fileIn.skipBytes(startpos);
-                readSize = startpos;
                 return this.startpos;
             } catch (IOException ioe) {
             }
         }
+
         return -1;
     }